RF electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart of concern. A typical renal ablation procedure involves the insertion of a catheter having an electrode at its distal end into a renal artery in order to complete a circumferential lesion in the artery in order to denervate the artery for the treatment of hypertension. A reference electrode is provided, generally taped to the skin of the patient or by means of a second catheter. RF (radio frequency) current is applied to the tip electrode of the ablating catheter, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. During this process, heating of the electrode also occurs as a result of conduction from the heated tissue to the electrode itself
Ablation of cardiac tissue using ultrasound energy, including High Intensity Focused Ultrasound (HIFU) energy has also been known for several years. In U.S. Pat. No. 7,201,749 entitled “Externally-applied high intensity focused ultrasound (HIFU) for pulmonary vein isolation” to Govari et al., an apparatus for the ablation of cardiac tissue is disclosed.
In U.S. Pat. No. 6,292,695 discloses a method of controlling cardiac fibrillation, tachycardia, or cardiac arrhythmia by the use of an electrophysiology catheter having a tip section that contains at least one stimulating electrode, the electrode being stably placed at a selected intravascular location. The electrode is connected to a stimulating means, and stimulation is applied across the wall of the vessel, transvascularly, to a sympathetic or parasympathetic nerve that innervates the heart at a strength sufficient to depolarize the nerve and effect the control of the heart.
The use of renal neurostimulation for the treatment of heart arrhythmias was disclosed in U.S. Patent Publication No. 2007/0129761, now abandoned, by Demarais et al. Demarais sets forth the use of neuromodulation to effectuate irreversible electroporation or electrofusion, ablation, necrosis and/or inducement of apoptosis, alteration of gene expression, action potential attenuation or blockade, changes in cytokine up-regulation and other conditions in target neural fibers. In some embodiments, such neuromodulation is achieved through application of neuromodulatory agents, thermal energy, or high intensity focused ultrasound.
In U.S. Patent Publication No. 2010/0222851, now U.S. Pat. No. 8,768,470, by Deem et al. the monitoring of renal neuromodulation was proposed stimulation to identify renal nerves to denervate or modulate. Stimulation of such nerves after prior to neural modulation would be expected to reduce blood flow while stimulation after neural modulation would not be expected to reduce blood flow to the same degree when utilizing similar situation parameters and locations prior to neural modulation.